[X86] Add x, t and g modifiers for inline asm

This patch adds the x, t and g modifiers for inline asm from GCC. These will print a vector register as xmm*, ymm* or zmm* respectively.

I also fixed register names with modifiers with inteldialect so they are no longer printed with a leading %.

Patch by Amanieu d'Antras

Differential Revision: https://reviews.llvm.org/D78977

(cherry picked from commit c5f7c039)